DNA separation plays a critical role in many genome projects, as well as in biochemistry and microbiology. However, conventional approaches for separation of DNA (e.g., gel electrophoresis) often require large reagent volumes, time-consuming manual preparation of the experimental setup, and long run times. For large DNA molecules, the standard separation method, pulsed-field gel electrophoresis (PFGE), is time consuming with analysis times ranging from hours to days. The technique also does not accommodate continuous flow in microfluidic devices because the gel sieving matrix must be replaced after separation. Other approaches to large DNA separation involve entropic trapping and tailored geometrically-structured micro devices, but the ease of application and obtainable separation resolution of these devices has not been tested, and it is questionable whether such techniques will be commercially viable.
Separation techniques have evolved to allow for the distinction and analysis of micro- and nanoscale particles such as nucleic acids, cells, viruses, and proteins. Microfluidic separation devices have utilized dielectrophoresis (DEP), field-flow fractionation (FFF), and combinations of the two (DEP-FFF). DEP refers to the phenomenon wherein subjecting a dielectric particle to a spatially non-uniform electric field will exert a force on the particle. DEP can be used to separate particles by taking advantage of the translational motion of a particle as a result of polarization induced by a non-uniform electric field. FFF involves selectively positioning particles in a liquid having a velocity profile to increase the separation of the particles as they travel downstream. Combined DEP-FFF involves using dielectrophoresis to position particles in a flow stream having a velocity profile.
Current microfluidic devices that use DEP and/or FFF are limited in performance by a reliance on gravitational effects for separation, a lack of sufficient interaction time to properly effect separation, and difficulty in separating complex mixtures having three or more components. Further improvements on current microfluidic separation techniques are desirable to allow for faster, more accurate, and more complex analysis of mixtures of particles.